Study On Degradation Of Nitrobenzene By The Synergies Of Electrochemically Active Bacteria And Quinoid-modified Polyurethane Foam

Nitrobenzene is considered as the optimal control pollution.There are four main treatment approaches with respect to nitrobenzene,including physical,chemical,biological and the combined,among which biological method is usually the preferred treatment technology,and anaerobic-aerobic biological method may be one of the most effective methods for the wastewater treatments.But metabolic rate for anaerobic microorganism is slow, so anaerobic biological treatment is usually bottleneck for complete biodegradation of nitrobenzene.Many researches found that some quinonoid compounds as redox mediators can accelerate electron transfer from electron donors to electronic receptors, so as to promote the anaerobic transformation of contaminants.However the drawbacks of these exogenous mediators in water treatment system are expensive, recalcitrant, and toxic as the effluent, which cause the secondary pollution. As a result, the effective immobilization of mediator and endogenous mediator from microorganisms are ideal options.Therefore, a new strategy for nitrobenzene transformation was proposed in this paper.We use redox mediator AQS with good catalytic performance covalently immobilized to the biological carrier-polyurethane foam(PUF),forming quinoid-modified polyurethane foam (Q-PUF).The synergies of a electrochemically active bacterium (Shewanella sp.XB) and catalytic carrier (Q-PUF) presented double enhancement effect and overcame the drawbacks of these exogenous mediators.The results of the experiments showed that the biomass of the immobilized electrochemically active bacteria on the Q-PUF,reached0.1g cell·g Q-PUF-1under appropriate conditions.Shewanella/Q-PUF can efficiently reduce nitrobenzene under anaerobic conditions, whose optimal degradation conditions are that carbon source is sodium lactate (10mM), nitrobenzene concentration is200mg·L-1pH of reaction is7,strain XB concentration is200mg·L-1.Nitrobenzene degradation rate by Shewanella/Q-PUF enhanced15times,reached4.1mM·g cell-1·h-1.Shewanella/Q-PUF degradation efficiency can keep over80%after repeated usage at optimal operating mode of MBR.LC-MS demonstrated intermediate product was hydroxylaminobenzene before6hour, which was transformed further into the final product of aniline.The cyclic voltammetry (CV) and fluorescence spectrophotometer revealed strain XB can secrete flavin.Q-PUF and PUF can promote flavin production by about1.5times than free strain XB.In addition strain XB could produce extracellular polymeric substances (EPS) which contained proteins, polysaccharides, nucleic acids, membrane lipids and fatty acids by FTIR analysis.UV-visible and fluorescence spectroscopy demonstrated the presence of cytochromes in bound EPS.And the EPS and flavin provided synergistic effect in nitrobenzene biotransformation.